This invention relates to a one-way clutch, and more particularly to a torque limiter-incorporating one-way clutch in which when the clutch is subjected to an overload in a locked state, the locked state is canceled.
One-way clutch is provided, for example, in a pulley unit of an engine auxiliary equipment driven by a crank shaft of an automobile engine through a belt. Examples of such engine auxiliary equipments include a compressor for an air conditioner, an alternator, a water pump and a cooling fan.
For example, there are various compressors for an automobile air conditioner, and in any of these compressors, rotating power of a crank shaft of an automobile engine is used as a drive source. The transmission of power from the crank shaft to a rotation shaft of the compressor is effected through a belt.
The rotation of the crank shaft varies according to a combustion cycle of the engine, and therefore a variation in rotation is transmitted from the crank shaft to the rotation shaft of the compressor. When this rotation variation increases, a variation in tension of the belt increases, and there is a fear that this tension variation of the belt can not be absorbed, and slip may develop between contact portions of the pulley and belt, so that the belt may be worn or damaged.
A pulley unit 1 for a compressor of an automobile air conditioner which is shown in FIG. 1 is connected to a crank shaft of an automobile engine via a belt 4 so as to transmit power of the engine to a rotation shaft 3 of the compressor 2. This pulley unit 1 comprises a pulley 5 having the belt 4 extended therearound, a hollow shaft 6 disposed within an inner periphery of the pulley 5 and fixed to the rotation shaft 3 of the compressor 2, a double row rolling bearing 7 (comprising an inner ring 71, an outer ring 72, a plurality of balls 73 arranged in two rows, and a cage 74 holding these balls 73) disposed between the inner periphery of the pulley 5 and an outer periphery of the hollow shaft 6, a closed-bottom cylindrical hub (one way clutch outer ring-support member) 9 fixed to an end portion of the rotation shaft 3 by a cap nut 8, and one-way clutch 10 (comprising an inner ring 75 integral with the outer ring 72 of the rolling bearing 7, an outer ring 76, a plurality of rollers 77 disposed between the inner and outer rings 75 and 76, urging members (not shown) respectively urging the rollers 77 in a biting direction, and a cage 78 having pockets respectively holding the rollers 77) disposed between an outer periphery of the outer ring 72 of the rolling bearing 7 and an inner periphery of a cylindrical portion 9a of the hub 9.
The outer ring 76 of the one-way clutch 10 is integrally connected to the rotation shaft 3 through the hub 9, and the inner ring 75 of the one-way clutch 10 is integral with the pulley 5. The pulley 5 is driven to be rotated by the belt 4, and power is transmitted from the pulley 5 to the rotation shaft 3 of the compressor 2 through the one-way clutch 10. When the speed of rotation of the pulley 5 becomes higher than that of the rotation shaft 3 of the compressor 2, the one-way clutch 10 is rendered into a locked state, and rotates the pulley 5, the hub 9 and the rotation shaft 3 in unison, that is, in synchronism with one another. In contrast, when the speed of rotation of the pulley 5 becomes lower than that of the rotation shaft 3 of the compressor 2, the one-way clutch 10 is rendered into a free state, and interrupts the transmission of rotating power from the pulley 5 to the rotation shaft 3 of the compressor 2, so that the rotation shaft 3 continues to rotate only with a rotation inertia force.
An ordinary one-way clutch does not has the function of interrupting the transmission of power from a belt to a rotation shaft of a compressor when an overload acts on the one-way clutch. Therefore, when an overload is applied, there is encountered a problem that the belt slips relative to the pulley, so that the belt is subjected to seizure and damage. Therefore, in order to solve this problem, there is proposed in JP-A-2002-106608 Publication a torque limiter-incorporating one-way clutch in which a recess for receiving a roller therein is formed in that portion of each cam surface disposed beyond a locking position on this cam surface, and when an overload is applied, each roller is restrained in the recess in such a manner that the roller does not function as a biting member, and as a result an outer ring and an inner ring become free relative to each other, thereby interrupting the transmission of power, thus performing the function of the torque limiter.
In this torque limiter-incorporating one-way clutch, when the rotation of a rotation shaft becomes abnormal, for example, as a result of a failure of a compressor due to seizure, a loading torque of the one-way clutch increases, and when this loading torque reaches a predetermined value (for example, 60 Nm), each roller is moved beyond the locking position into a still narrower portion of a wedge-like space, and is fitted into the recess in the cam surface, so that each roller is disposed in a non-contact condition or idles relative to the pulley. As a result, the only the pulley rotates, and the transmission of the power from the pulley to the rotation shaft of the compressor is interrupted, thereby performing the function of the torque limiter.
In the torque limiter-incorporating one-way clutch of JP-A-2002-106608 Publication, when an overload is applied, the rollers are fitted respectively into the recesses, thereby canceling the locked state, and as a result the transmission of the power from the belt to the rotation shaft of the compressor is interrupted, and therefore the problem with respect to seizure and damage of the belt is solved. However, the following problem must be solved in order to secure a more positive power-interrupted condition. Namely, when the torque limiter is operated, a clearance develops between each roller and a corresponding spring (urging member) urging it, and the springs are not retained by any part, and therefore the springs become free, and this leads to a possibility that the springs are bitingly held between an outer ring and an inner ring. In this case, the one-way clutch can be returned to a normal condition in which power is again transmitted, and therefore it is necessary to prevent each spring from being bitingly held between the outer ring and the inner ring.
In the torque limiter-incorporating one-way clutch of JP-A-2002-106608 Publication, when an overload is applied, the rollers are fitted respectively into the recesses, thereby canceling the locked state, and as a result the transmission of the power from the belt to the rotation shaft of the compressor is interrupted, and therefore the problem with respect to seizure and damage of the belt is solved. However, the following problem must be solved in order to secure a more desirable torque limiter function. Namely, with respect to the positioning of the inner and outer rings of the torque limiter-incorporating one-way clutch, there are many deviations factors such as concentricity of the compressor shaft (rotation shaft) (to which a hub having the outer ring mounted thereon is fixed) with the inner ring serving also an outer ring of a bearing mounted on a compressor body, deviations developing during an assembling operation, etc., and there is a possibility that positioning precision is worsened, so that an operating torque for operating the torque limiter is much varied.
In the torque limiter-incorporating one-way clutch of JP-A-2002-106608 Publication, when an overload is applied, the rollers are fitted respectively into the recesses, thereby canceling the locked state, and as a result the transmission of the power from the belt to the rotation shaft of the compressor is interrupted, and therefore the problem with respect to seizure and damage of the belt is solved. However, the following problem must be solved in order to secure a more positive power-interrupted condition. Namely, when the rollers are to be fitted into the respective recesses, slip (engagement slip) occurs because of a reduced friction coefficient, and this leads to a possibility that the one-way clutch is damaged or broken by popping. Therefore, it is necessary to prevent such engagement slip.
In the torque limiter-incorporating one-way clutch of JP-A-2002-106608 Publication, when an overload is applied, the locked state is canceled, thereby interrupting the transmission of power from the belt to the rotation shaft of the compressor, and therefore the problem with respect to seizure and damage of the belt is solved. However, it is necessary to additionally form the recesses in the cam surfaces, and therefore it is required to increase the overall size or to reduce the number of the rollers if the size can not be increased, which has invited a problem that a torque capacity is decreased,
JP-A-2003-028201 Publication discloses a roller-type one-way clutch in which lock cancellation recesss serving as a torque limiter function are formed in cam surfaces of the one-way clutch. In this torque limiter, when an overload develops, engagement rollers roll to be fitted into the respective lock cancellation recesss, thereby interrupting a torque.
FIGS. 15A and 15B are a side cross-sectional view and a front cross-sectional view of a conventional one-way clutch unit 200. This one-way clutch unit 200 includes a single-row one-way clutch 108 and a single-row support bearing 109 (in the form of a single-row ball bearing) which are disposed adjacent to each other in an axial direction. The one-way clutch unit 200 includes a one-piece outer ring 181, and a one-piece inner ring 172. The one-piece outer ring 181 includes a clutch outer ring portion 181a for the one-way clutch 108 and a bearing outer ring portion 181b for the support bearing 109 which are integral with each other. The one-piece inner ring 172 includes a clutch inner ring portion 172a for the one-way clutch 108 and a bearing inner ring portion 172b for the support bearing 109 which are integral with each other. The one-way clutch 108 includes engagement rollers 183 serving as wedge members. The clutch outer ring portion 181a of the one-piece outer ring 181 has a cylindrical inner peripheral surface, and the clutch inner ring portion 172a of the one-piece inner ring 172 has a cam surface 176 of an octagonal cross-section. Lock cancellation recesss 177 are formed in the cam surface 176. The one-way clutch 108 and the support bearing 109 are lubricated with the same grease sealed between the one-piece outer ring 181 and the one-piece inner ring 172, and seal members 111 and 112 are disposed between the one-piece outer ring 181 and the one-piece inner ring 172 at axial opposite end portions of the unit, and seal the grease. The one-way clutch 108 further includes a cage 182 holding the engagement rollers 183 in such a manner that the engagement rollers 183 are urged in one direction by urging springs (coil springs) 184, respectively. The cage 182 has pockets 182a in which the engagement rollers 183 are fitted, respectively. The support bearing 109 includes a crown type cage 117 holding balls (rolling elements) 116. In the one-way clutch 108, when an excessive torque develops, the engagement rollers 183 roll, and are fitted into the respective lock cancellation recesss 177, utilizing elastic deformation of the one-piece inner ring 172, one-piece outer ring 181 and engagement rollers 183, thereby interrupting the torque. Such a one-way clutch will hereinafter be referred to as “torque limiter-incorporating one-way clutch”.
In the conventional torque limiter-incorporating one-way clutch, when an excessive torque develops, the engagement rollers rolls, and are fitted respectively into the respective lock cancellation recesss, utilizing elastic deformation of the one-piece inner ring, one-piece outer ring and engagement rollers, thereby interrupting the torque. However, variations in dimensions of the inner ring, outer ring, engagement rollers, etc., are large relative to the amount of elastic deformation (that is, dimensional accuracies are low), a variation (deviation) in the torque limiter-operating torque becomes large, and this invited a problem that the torque limiter function could not be performed just when this was desired.
It is an object of this invention to provide a one-way clutch in which the precision of a torque limiter operating-torque is enhanced so that a torque limiter function can be performed just when this is desired, and also to provide a one-way clutch unit having a support bearing formed integrally with a one-way clutch.